408 



JOHNSON AND BRINTON 



CHAP. 18 



the Beaufort Sea, and the two species discussed in the next paragraph were 

 transported in such a water stratum. 



A recent analysis of zooplankton collected in 1957-58 during the drift of 

 the ice floe "Drift Station Alpha" in latitudes 81° 14'N to 85° 16'N shows 

 additional expatriate species from the North Pacific Ocean-Bering Sea popula- 

 tions (Johnson, MS). Individual adults of Eucalanus bungii bungii Giesbrecht 

 were taken at 83° 41'N, 155° 13'W and at 85° 6'N, 167° 40'W. This same 

 species was also reported by Brodskii and Nikitin (1955) at 77° 5'N and 

 80° 51'N. Another species, Mimocalanus distinctocephalus Brodskii, occurred in 

 the ice floe collection taken at 83° 4'N and is probably an expatriate there. 

 Brodskii (1957) found it at 50% of the oceanic stations from 500- to 1000-m 

 depths in the Bering Sea. 



Under conditions of cooling associated with northward flow of Pacific and 

 Bering Sea water, the survival of contained southern species far beyond their 

 endemic area would be enhanced by the drop in temperature. That this might 

 occur is supported by the experiments carried out by Clarke and Bonnet (1939) 

 in which the survival of Calanus finmarchicus was definitely better at 3°C than 

 at temperatures of 6° and 9°C. 



E 

 73° N 



^77777777777 



DSW . ' 



7777777777777777777777777T7777 



87 



162 160 



Fig. 12. Water-mass structure from Cape Lisbourne to the ice pack, based on temperature 

 and salinity relations. See Fig. 11 for position of section E-E'. 



ACW, Alaskan Coastal Water ; MSW, Modified Shelf Water ; MIM, Modified Ice 

 Melt; IM, Ice Melt; DSW, Deep Shelf Water. This DSW is not considered con- 

 tinuous with the Bering Sea as are the others. (After Saur, Tully and LaFond, 1954.) 



The northward and eastward extensions of the U.S.S. Burton Island collec- 

 tions in the Chukchi and Beaufort Seas make it also possible to consider here, 

 in contrast, the distribution of two characteristically arctic species of copepods 

 — Calanus hyperboreus and Metridia longa. The southern limit of distribution 

 observed for these species shows that a good deal of overlapping of areas may 

 occur (Fig. 11), but the main population of arctic species is held back in the 

 Chukchi Sea by the flow from the Bering Sea. A broad transition zone seems to 

 exist in the northern Chukchi Sea, if one may judge by the 1947 and 1951-1952 

 collections. The position and extent of this zone doubtless varies somewhat 

 from year to year. In the Beaufort Sea area the truly arctic zone is more 

 sharply defined east of Point Barrow where there is, however, a clear over- 

 lapping of the arctic and the more southern species, suggesting considerable 



